The present invention relates to a current measuring device. More particularly, the present invention relates to a device that measures electric current in a conductor and produces a frequency output signal responsive thereto.
Controlling pumps, compressors, heaters, conveyors, and other electrically powered loads requires accurate, real-time status feedback. Current sensing is a reliable and economical way to monitor and control electrically powered loads. Current transducers are commonly used to accurately measure the electric current in a conductor. Single piece non-contact current transducers measure AC or DC current in the conductor and output a proportional analog signal in response to the presence of current in the conductor. The types of analog signals generally include DC voltage (0-5V or 0-10V), AC voltage (0-0.33V up to 0-10V) or a DC current (0-1 mA, 0-20 mA or 4-20 mA).
Current sensors are frequently used to provide essential information to automated control systems, and as primary controllers in relay logic schemes. Because current transducers can be connected directly to data systems and display devices, they are ideal for monitoring motors, pumps, conveyors, machine tools, and any electrical load that requires an analog representation over a wide range of currents.
However for an automation system to read this type of analog output, it must be equipped with an analog input (AI) card. An AI card usually includes terminals, signal conditioning and analog to digital conversion (ADC). The analog signal is converted into a digital word that quantifies the analog level. The AI cards are expensive. Adding a single analog input can add several hundreds of dollars in cost. This makes analog inputs cost prohibitive in many installations.
The other generally available automation system input is a digital input (DI). DI reads simple contact closures. Many systems are only equipped with DI and cannot be fitted with an analog input card at all. For these systems, reading true analog inputs is impossible. However, many of the digital inputs in these systems incorporate high speed counters. These counters take a rapidly switched signal having a particular frequency and convert it into a digital word. This digital word can perform the same function as the word produced by an AI card. For these types of systems, an analog signal generated by a current sensor must be converted to a frequency (series of contact closures) in a separate signal conditioning component.
Accordingly, a need exists for a measuring device that integrates a sensor, a signal conditioner and a frequency output into a single device. The measuring device should be compact, inexpensive, and easy to install.
A device measures current magnitude in a conductor coupled to an electrical device and generates a signal comprising a series of pulses having a frequency. The frequency of the series of pulses is responsive to the magnitude of current measured. The device comprises a sensor magnetically linked with the conductor connected to the electrical device. The sensor produces an analog signal in response to the presence of a current within the conductor. A signal conditioner is located proximate to the sensor and is electrically coupled to the sensor so as to receive the analog signal. The signal conditioner produces, in response to the analog signal, a first signal representative of a magnitude of the current. A converter receives and converts the first signal into an output signal that comprises a series of pulses having a frequency. The frequency of the series of pulses is responsive to the magnitude of the current. All the sensor, the signal conditioner, and the converter are located in a single unitary package.